FIELD OF THE INVENTION
The present invention generally relates to fluidized bed coal gasification /
combustion systems. More particularly, the present invention relates to a water
cooled distributor with screw type bubble cap nozzles for air / steam distribution
in high pressure fluidized bed gasification systems to improve the overall
efficiency of the systems.
BACKGROUND OF THE INVENTION
Pressurized Fluidized Bed Gasifiers generate fuel-gas from coal, lignite or other
carbonaceous solid fuels, for use in power, process and chemical applications. In
a refractory lined pressurized fluidized bed gasifier, during gasification process,
the crushed coal is continuously injected into the bed, air or a mixture of air and
steam is introduced through a distributor located at the bottom of the gasifier,
the coal with bed material is uniformly fluidized with adequate fluidization

velocity with the help of bubble cap air / steam nozzles. By a chemical reaction, a
stream of high-pressure and high-temperature raw synthesis gas also called
"Syngas" is generated with specific chemical composition and calorific value. A
plurality of bubble cap nozzles located at predetermined locations in the
distributor fluidize the bed and allows the coal to mix rapidly and thoroughly. The
hot combustion gas is supplied to the combustor of a gas turbine engine, which
powers a generator that supplies electrical power to a power grid. Exhaust from
the gas turbine engine is admitted to a heat recovery steam generator that
generates steam for driving a steam turbine. Power generated by the steam
turbine also drives an electrical generator that provides electrical power to the
power grid.
According to the prior art shown in Fig.l, the distributor comprises; a plurality of
bubble cap nozzles (01) welded to a number of stubs (02) for fluidizing and
thorough mixing of the bed, a number of distributor plates (03) in which the

stubs (02) with nozzles (01) are welded for holding the bed at high temperature
and pressure, a plurality of cooling water pipes (04) welded to the distributor
plates (03) in such a fashion so that cooling water enters at one end and leaves
at the other end; and a pipe (05) welded at the centre of the distributor to
remove the bottom ash. The configuration and connectivity of the welded type
bubble cap nozzles (cap and stub welded together) create problems in leak
checking of stub welding joints and removing of failed bubble cap nozzles for
replacement with new nozzles involve gas cutting, grinding, welding and leak
checking of stubs weld joints. This tedious work takes a very long time.
Gasification of coal is necessary to generate electricity through an integrated
gasification and combined cycle using various grades of coal.
Typically, in pressurized fluidized bed gasifiers, air or a mixture of air and steam
is admitted from the bottom of the gasifier. The coal with bed material is

uniformly fluidized with adequate fluidization velocity with the help of bubble cap
air nozzles. By the chemical reaction, coal gas is formed with specific chemical
composition. The distributor allows fluidization of the bed and mix the coal
rapidly and thoroughly. During the gasification process, over a period of time,
problems are encountered due to failure of the bubble cap nozzles (deformation
and melting of bubble cap nozzles), and localized over heating at few places in
the distributor. Removing of failed bubble cap nozzles and replacing of the failed
ones with new nozzles involve gas cutting, edge preparation by grinding and
welding. These cumbersome work take a very long time. To overcome these
problems, an improved nozzle is envisaged and a water cooled distributor with a
screw type bubble cap nozzles for air / steam distribution in high pressure
fluidized bed gasification system appears to be the technical solution of the prior
art disadvantage.

US Patent No.4429471 dated Feb. 7, 1984, entitled "FLUIDIZED BED AIR
DISTRIBUTOR" discloses a fluidized bed apparatus comprising a fluidized
chamber having a grid plate below said chamber, a feed gas channel below said
grid plate, and a fluidized bed distributor, said fluidized bed gas distributor
comprising a nipple, a cap and a bushing, wherein said cap is provided with at
least one gas distribution passage, and said nipple includes a central nipple
passage and said bushing includes a central bushing passage, said cap being
attached to a first end of said nipple said bushing being attached to a second
end of said nipple.
Whereas "a water cooled distributor with screw type bubble cap nozzles for air /
steam distribution in high pressure fluidized bed gasification system" differs by
design / construction point of view from the cited U.S. Patent.

OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a water cooled
distributor with screw type bubble cap nozzles for air / steam distribution in high
pressure fluidized bed gasification system, which reduces the repair and
maintenance time by avoiding drawbacks of the current art.
Another object of the present invention is to propose a water cooled distributor
with screw type bubble cap nozzles for air / steam distribution in high pressure
fluidized bed gasification system, which provides easy leak checking of stubs
(nozzle holder welded to the distributor) welding joints by using dummy
washers.
A still another object of the present invention is to propose a water cooled
distributor with screw type bubble cap nozzle for air / steam distribution in high
pressure fluidized bed gasification system, which allows easy removal and
replacing of new bubble caps to meet the desired pressure drop across the
bubble cap nozzles.

Yet another object of the present invention is to propose a water cooled
distributor with screw type bubble cap nozzles for air / steam distribution in high
pressure fluidized bed gasification system, which enables uniform flow
distribution with adequate nozzle velocity for large gasifiers (diameter more than
1 metre).
A further object of this invention is to propose a water cooled distributor with
screw type bubble cap nozzles for air / steam distribution in high pressure
fluidized bed gasification system, which minimizes the formation of agglomerates
by rapid and thorough mixing of bed and also to aid for easy extraction of bed
ash.
SUMMARY OF THE INVENTION
Accordingly, there is provided a device for water cooled distributor with screw
type bubble cap nozzles for air / steam distribution in high pressure fluidized bed
gasification system comprising; a cylindrical shaped fluidizing bed chamber

enclosed by a refractory brick lining to withstand high temperature, a non-
fluidized bed material uniformly spread over a number of flat plates and act as a
thermal insulator and protects the flat distributor plates from high temperature, a
plurality of screw type bubble caps having a plurality of fluidizing nozzles with
desired pitch drilled at the top periphery of the caps for fluidizing the bed, a
plurality of internal threads machined at bottom end and a spanner holding slot
provided at the top end of the caps, a plurality of stubs having corresponding
external threads machined at top end and the other end is attached to the
distributor plates by a number of welds, a number of cooling water tubes welded
with a number of bends rigidly attached to the distributor plates provides cooling
water circuit, the cooling water enters at one end and leaves at the other end, a
pipe welded at the centre of the distributor allows removal of the bottom ash
and a plurality of dummy washers placed firmly in between the bubble caps,
wherein the stubs to arrest the air flow through nozzles only during leak
checking of weld joints.

The configuration and connectivity of the proposed distributor reduces the repair
and maintenance time and provides an easy leak checking of the stubs (nozzle
bottom welded to the distributor) welding joints by using dummy washers.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 - shows a cross-sectional view of a device according to the prior art.
Fig. 2 - shows a cross-sectional view of a water cooled distributor with a screw
type bubble cap nozzles for air / steam distribution in high pressure fluidized bed
gasification system, according to the present invention.
Fig. 2a - shows a cross-sectional and enlarged view of a screw type bubble cap
nozzle, according to the present invention.

Fig. 3 - shows a plan view of a water cooled distributor with screw type bubble
cap nozzle for air / steam distribution in high pressure fluidized bed gasification
system, according to the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
PRESENT INVENTION
According to the present invention, and as shown in Figs.2,2a, and 3, there is
provided a water cooled distributor with screw type bubble cap nozzles for air /
steam distribution in high pressure fluidized gasification "bed" system,
comprising; a fluidizing bed chamber (06) enclosed by a refractory brick lining
(07) to withstand high temperature and high pressure fluidized bed; a non-
fluidized bed material (08) uniformly spread over a plurality of flat distributor
plates (15) to act as a thermal insulator and protect distributor plates (15) from
high temperature; a plurality of screw type bubble caps (09) having a
plurality of fluidizing nozzles (10);a plurality of drilled holes configured at the top

periphery of the caps (09) through which the feed air or a mixture of air and
steam is uniformly distributed at optimum velocity for fluidizing the material in
the fluidizing bed chamber (06), in particular for large gasifiers (diameter more
than 1 metre). In order to minimize the formation of agglomerates by rapid and
thorough mixing of bed, and further to ensure easy extraction of bed ash, a
plurality of internal threads (11) machined at bottom end and a spanner holding
slot (12) are provided at the top end of the caps (09); a plurality of stubs (13)
having corresponding external threads (14) machined at top end with the other
end being attached to the distributor plates (15) by number of welds (16); a
number of cooling water tubes (17) welded with matching number of bends (18)
welded to the distributor plates (15) as shown in Fig.3 form a cooling water
circuit, the cooling water enters at one end and leaves at the other end, a pipe
(19) welded at the centre of the distributor (15) to remove the bottom ash; a

plurality of dummy washers (20) placed firmly In between the bubble caps (09)
and the stubs (13) to arrest the pressurized air flow through the nozzles (10)
only during leak checking of weld joints (16). The step of leak check is vital
because, if the pressurized air leak through the weld joints (16), the air jet will
create localized burning, high temperature and erosion of stubs in the non-
fluidized bed zone and finally damage the bubble cap nozzles. Once the leak
check is done successfully and no leakage of air is found in the weld joints (16),
it avoids localized burning, high temperature and erosion of stubs in the non-
fluidized bed zone, also avoids erosion deformation of bubble caps.
The internal threads (11) provided at the bottom of the caps (09) screwed into
the top external threads (14) of the stubs (13) to attach the caps to the stubs
(13), the spanner holding slot (12) provided at the top end of the caps (09)
allows the caps (09) to be tightly screwed into the stubs (13).

The bubble caps (09) are supported by the distributor plates (15). The cooling
water circuit (17, 18) safeguards the distributor plates (15) during bed heating
process by hot flue gases from an oil burner.
The distributor assembly with the plurality of bubble caps (09) and stubs (13) is
fixed / welded at the bottom of the gasifier and the cooling water inlet and outlet
connections are made. It holds the beds to a particular height with high
temperature.
The advantage of this system is that when a high pressure drop is desired across
the distributor nozzles (10); the caps (09) are removed and plug weld few
nozzles and put back or new caps with smaller diameter nozzles can be quickly
inter-changed and vice versa.
The air or air and steam mixture is introduced through the bottom of the water
cooled distributor, coal is injected to the gasifier through ejector using
compressed air and the bed material is already filled in the gasifier

During the gasification process, the distributor creates uniform flow distribution
of air and steam mixture and ensures uniform temperature distribution above the
bed which in turn enables to produce correct composition of fuel gas. It
minimizes or avoids the formation of agglomerates by rapid and thorough mixing
of the bed with the help of bubbles cap air / steam nozzles. It also holds the bed
to a particular height with high temperature by allowing easy bed ash removal, it
maintains uniform fluidization velocity and the cooling arrangement enables the
distributor to withstand high temperature. The invention substantially reduces
the repair and maintenance time and cost and provides easy leak checking of
stubs welding joints by using dummy washers.

WE CLAIM:
1. A water cooled distributor with screw type bubble cap nozzles for air /
steam distribution in a high pressure fluidized bed gasification system,
comprising:
a shaped fluidizing bed chamber (06) enclosed by a refractory brick lining
(07) to accommodate the high pressure and temperature fluidized bed;
a non-fluidized bed material (08) uniformly spread over the distributor
acts as a thermal insulator and protects the distributor from high temperature;
and
a plurality of screw type bubble caps (09) having a plurality of fluidizing
nozzles (10) to feed air or a mixture of air and steam and uniformly distribute at
optimum velocity for fluidizing the material in the fluidizing bed chamber (06)
such that the formation of agglomerates is minimized by rapid and thorough
mixing of the bed material including easy extraction of bed ash.

2. The water cooled distributor as claimed in claim 1, wherein a plurality of
internal threads (11) are provided at the bottom of the caps (09) so that the
caps can be screwed into top external threads (14) of corresponding number of
stubs (13) to attach the caps to the stubs.
3. The water cooled distributor as claimed in claim 1 or 2, wherein a spanner
holding slot (12) is provided at the top end of the caps (09) to screw the caps
(09) tightly into the stubs (13).
4. The water cooled distributor as claimed in any of the preceding claims,
wherein a first plurality of said plurality are vertically attached to the distributor
by a number of welds (16).
5. The water cooled distributor as claimed in claim 1, wherein the plurality of
flat distributor plates (15) having a number of holes in which the bottom ends of
the stubs (13) are inserted and firmly fixed by said number of welds (16).

6. The water cooled distributor as claimed in claim 1, comprising a plurality
of cooling water pipes (17) having a number of bends (18) are welded to the flat
distributor plates (15) to form a cooling water circuit, the cooling water enters at
one end and leaves at the other end of the circuit.
7. The water cooled distributor as claimed in claim 6, wherein the flat plates
(15) are welded in between the plurality of cooling water pipes (17) to form a
water cooled distributor.
8. The water cooled distributor as claimed in claim 6, comprising a pipe (19)
located and welded at the centre of the distributor for bottom ash extraction.
9. The water cooled distributor as claimed in claim 8, wherein a plurality of
dummy washers (20) are placed firmly in between the bubble caps (09) and the
stubs (13) to arrest the air flow through the nozzle (10) during leak checking of
the weld joints (16).

10. The water cooled distributor as claimed in claim 9, wherein the bubble cap
nozzles (09) are supported by the distributor plates (15).

A water cooled distributor with screw type bubble cap nozzles for air / steam
distribution in a high pressure fluidized bed gasification system, comprising: a
shaped fluidizing bed chamber (06) enclosed by a refractory brick lining (07) to
accommodate the high pressure and temperature fluidized bed; a non-fluidized
bed material (08) uniformly spread over the distributor acts as a thermal
insulator and protects the distributor from high temperature; and a plurality of
screw type bubble caps (09) having a plurality of fluidizing nozzles (10) to feed
air or a mixture of air and steam and uniformly distribute at optimum velocity for
fluidizing the material in the fluidizing bed chamber (06) such that the formation
of agglomerates is minimized by rapid and thorough mixing of the bed material
including easy extraction of bed ash.